It is known to use subsea buoys in hydrocarbon production facilities. These buoys are tethered to the seabed with mooring chains in order to maintain them in a desired position. The chains are connected to the buoys by way of connector assemblies which can accommodate a chain tensioner to enable the tension in a mooring chain connected to the connector assembly to be adjusted.
A connector assembly is disclosed in GB 2496860. The assembly comprises a support mounted to a subsea buoy. A lever member is mounted to the support by way of a flex joint allowing the lever to move relative to the support about a pivot axis. A chain stop mechanism is mounted to the support below the pivot axis. A frame rests on and extends above the support and a sheave is mounted to the frame at a position above the pivot axis. In use a chain extends from the sea bed into the chain stop mechanism, up through the lever member and over the sheave with the free end of the chain hanging down from the sheave. A chain tensioning unit may be supported on top of the support, at a position above the pivot axis, and arranged to tension the chain to enable tension in the chain to be adjusted.
The chain stop mechanism prevents downward movement of the chain through the lever member and so, in normal use, maintains tension in the chain between the sea bed and the buoy. The flex joint allows the lever member to pivot relative to the buoy under tension in the chain so that the chain extends in a substantially straight path from the seabed to the chain stop mechanism as the buoy moves relative to the sea bed, thus avoiding undesirable stress concentrations in the chain.
When it is desired to adjust tension in the chain a chain tensioner unit is placed onto the support. The chain tensioner unit includes jacks which engage with the chain extending from the lever member to the sheave in order to tension the chain and draw it up through the chain stop mechanism to either increase tension in the chain between the chain stop mechanism and the sea bed or, by taking load off the chain stop mechanism allowing it to be released, to decrease tension by allowing chain to pass downwardly through the chain stop mechanism.
A problem has, however, been found with the assembly in that when the chain tensioner unit takes up load on the chain undesirable stress concentrations can build up in the chain. Since the chain tensioner unit is in a fixed position relative to the support the chain may no longer extend in a substantially straight path between the point at which it is supported (i.e. the chain tensioner unit) and the sea bed. Additionally, the chain may no longer extend in a straight path from the chain tensioner unit and the lever member which can make it difficult to disengage the chain tensioner and/or cause damage to the lever member. These issues cause additional wear on the chain, potentially leading to its premature failure.
Embodiments of the present invention have been made in consideration of these problems.